In the art of ophthalmic lens manufacture, a finished ophthalmic lens is usually made from finished uncut lenses or from semi-finished lens blanks. Finished uncut lenses are lenses that are optically finished on both front and back surfaces and only need to be edged to the proper shape and edge contour to become finished lenses. Most optical laboratories keep an inventory of single vision finished uncut lenses in various powers, sizes, and materials to take care of most of the more common single vision ophthalmic lens prescriptions.
Semi-finished lens blanks have optically finished front surfaces; however, the back surfaces of these blanks need to be generated and fined and are then either polished or coated to produce finished uncut lenses. Finished uncut lenses are then edged to the proper frontal shape and edge contour to fit into spectacle/glasses frames or other mounting structures. Single vision lenses that are outside the normal range of inventoried finished uncut lenses and most multifocals are made from semi-finished lens blanks. Semi-finished lens blanks are made with various front surface curve radii, and have various topographies including spherical, aspheric, hyperbolic, irregular aspheric such as progressive add lenses, and polyspheric such as executive type segmented bifocals and trifocals.
To generate a desired prescription for a lens, calculations are required to determine the topography of the back surface of a lens. Such calculations typically involve variables that include the front surface radii of the semi-finished blank, the index of refraction of the lens blank material, prescription values of the desired lens, statutory values regarding minimum lens thickness, and the physical dimensions of the frame or mounting structure.
In the art, various means have been devised to accomplish the physical process of producing a back surface of optical quality. Most of these methods begin by generating a back surface that approximates the desired back surface topography and surface smoothness. This approximate surface is then fined to a more perfect approximation in both curvature and surface smoothness. After the appropriate accuracy and smoothness is achieved in the fining process, the surface is then polished or surface coated to produce a surface of optical quality. The optically finished lens blank is then edged to the proper shape and edge profile to fit into the frame for which it was made.
Many business entities that sell ophthalmic lenses do lens finishing as a profit center activity and as a way to expedite delivery of single vision lenses. Only a small percentage of these entities also do surfacing of ophthalmic lenses. The business volume of most of these entities cannot justify the costs of acquiring and operating a surfacing laboratory. Surfacing laboratory setup costs have heretofore been several times the cost of setting up a laboratory for edging only.
Hiring qualified technicians for ophthalmic lens finishing or training personnel to perform ophthalmic lens finishing is relatively easy. However, hiring and training optical technicians to operate a surfacing laboratory is not easy. In many communities it is very difficult to find personnel that are trained in surfacing. Technicians who are qualified to do surfacing are generally remunerated at higher pay scales than technicians skilled only in optical finishing.
In addition to the significantly higher equipment and personnel costs of a surfacing lab, there are also higher ongoing costs for the additional lab space required. At least several hundred square feet of operational space and storage space have heretofore been required for a full service surfacing and edging ophthalmic lens laboratory. Consequently there is a need for a system and method of ophthalmic lens manufacture that would significantly reduce the investment required to acquire a surfacing and edging laboratory. There is a further need for a system and method of ophthalmic lens manufacture that significantly reduces the costs associated with operating a surfacing and edging laboratory. Further, there is a need for a system and method of ophthalmic lens manufacture that is operative to perform surfacing and edging by an operator with little skill in the art.
In the prior art, the processes of surfacing and edging are done on at least two separate machines. In the prior art, blocking for surfacing and edging required two separate blocking devices. Also in the prior art, the individual processes of lap tool surfacing and lens cribbing and safety beveling and edge grooving and edge polishing and lens engraving each requires its own machine or device or machine augmentation. Each of these machines or devices or augmentations is to varying degrees expensive to acquire and each of the machines or devices requires laboratory space. Each of these operations, if done by hand, requires the necessary acquisition of skills and application of those skills in order to perform the various operations. Consequently, there is therefore a need for a system and method of ophthalmic lens manufacture that reduces the need to employ a plurality of expensive and complex machines to manufacture lenses.
In the prior art, after a semi-finished lens blank is generated and fined and polished it is de-blocked and inspected and then laid out and blocked again for edging. Blocking for surfacing and blocking for edging are two different procedures that differ in significant ways requiring two different sets of skills and requiring two separate and very different mechanical blocking systems. Repeating the blocking process is necessary in part because the metallic block used for surfacing could interfere with the edging process. This is because portions of the uncut lens that lie under the surfacing block frequently need to be removed during the edging process. If the standard surfacing block were also used during edging, this could result in the metal surfacing block coming into contact with the cutting or grinding surfaces of the edging machine thereby damaging the cutting or grinding surfaces of the edging machine and damaging or destroying the block in the process. Additionally, the need to block a lens twice multiplies the opportunities for error and spoilage and requires the expenditure of time. Consequently there is a need for a method of ophthalmic lens manufacture that eliminates the need to block a lens blank twice for those lenses that require both surfacing and edging.
The prior art describes several types of single point blocking systems. One type describes centering the block on the point of the lens that would occupy the geometric center of the frame when the lens is finished (frame geometric center blocking). Another describes centering the block on the point of the lens that would occupy the optical center of the finished lens (optical center blocking). A third describes centering the block in the geometric center of the semi-finished uncut lens (lens blank geometric center blocking). In prior art, all three of methods are optimized for surfacing by tilting the front surface by the proper amount and in the proper direction to move the optic axis into alignment with the generator feed axis. Only in the case of “frame geometric center blocking” is it possible to optimize for edging. This optimization for edging is accomplished by aligning the front surface normal at the geometric center with the feed axis of the generator.
The “optical center” and “lens blank geometric center” blocking arrangements create relationships between a lens blank and the generator feed axis that are optimal for generating lens back surfaces because errors in thickness at any stage in the process of surface generation and fining will not affect a change in the position of the optical center of the lens. This is because the optic axis does not move as the thickness of the blank decreases. However, in neither of these two cases are the blocking arrangements optimal for edging a lens. In both instances the lens is frequently tilted too much to apply an edge parallel to the normal at the geometric center of the front surface of the finished lens. Applying an edge to a lens at any angle other than parallel to the front surface normal at the geometric center results in edges that are skewed and frequently thicker than necessary and with edge beads that have less than optimal orientations.
A blocking system optimized for edging, like “frame geometric center blocking”, wherein the lens blank is blocked on the geometric center of the finished lens and where the normal at the geometric center of the front surface of the finished lens is parallel to the axis of rotation of the edging tool or edge grinding wheel, is not optimal for surfacing. Except for the relatively rare case where there is positional coincidence between the optical center of the lens and the frame geometric center of the lens, the optical center of the lens is made to move or “creep” as the lens is made to decrease in thickness during fining.
A method of lens blocking that is optimized for edging and that is also operative for surface generation would be of considerable utility. It would allow for a single blocking step for both the surface generation of a lens and for the edging of that lens without de-blocking and re-blocking between the steps of surface generation and edging. Therefore there is a need for a system and method of blocking a lens for both surfacing and edging that reduces the problems associated with optical center creep.
Prescription lenses for patients are often generated in pairs for a spectacle frame. Prior art systems typically generate each lens independently. Production cycle times for generating lenses may be reduced by employing multiple surfacing and edging machines in the laboratory to generate pairs of lenses simultaneously, however duplication of equipment doubles the acquisition and operational costs of the laboratory. Thus there exists a need for a system and method of ophthalmic lens manufacture that provides for reduced production cycle times for pairs of prescription lens without significantly increasing costs for the laboratory.
Heat transfer into the lens blank from the heated blocking medium during the blocking procedure is a frequent cause of so called “lens warpage”. The greater the amount of heat transfer involved and the more uneven the distribution of that heat transfer is, the greater the chance of producing warpage and ruining the lens or producing a substandard lens. There is therefore a need for a method of ophthalmic lens manufacture that could minimize the transference of heat into the lens blank during blocking, and that could make the distribution of that heat transference uniform over the entire area of the finished lens. Further, there is a need for a system and method of ophthalmic lens manufacture that could eliminate problems associated with heat transfer into the lens during blocking.
The standard block used for lens surfacing is generally smaller than the size of the finished lens being fabricated. The portion of a lens that remains unsupported can undergo flexure when submitted to the forces involved in the generating, fining and polishing processes. This results in flaws or “waves” in the optics of the lens in the areas that underwent the flexure and is a common source of spoilage or of substandard lenses. Consequently, there is a need for a technique that would eliminate these optical flaws caused by flexion of the lens blank during generating and fining and polishing of the lens.
For cosmetic effect, the edges of lenses are sometimes polished. In prior art, when the edge of the lens has a mounting bevel, the bevel on the edge of the lens is polished when the edge is polished. Polishing the mounting bevel reduces the holding friction of the bevel that aids in holding the lens in the frame, and that holding friction is also important in resisting rotation of the lens within the frame. For this reason, a lens that has a polished edge with a polished bevel is more difficult to keep securely mounted and properly oriented in its frame. There is therefore a need for a system and method of ophthalmic lens manufacture that is operative to polish the edge of a lens without polishing the mounting bevel on the edge of the lens.
Prior art systems for lens manufacture are inherently non-mobile, due to the large amounts of laboratory space required to store an inventory of lap tools and the many pieces of heavy laboratory equipment needed to generate and surface and finish lenses. Thus, prior art systems cannot be easily transported to locations such as factories to manufacture safety lenses on-site or military theaters to support the optical needs of military personnel. Consequently, there is a need for an ophthalmic lens manufacturing system that is portable.